I also noticed that if you use Windows Server DHCP you need to add Server options for DHCP as follows:

066 Boot Server Host Name:: ip or host name of FOG server
067 Bootfile Name: ipxe.efi (for UEFI system)

So do not use snponly.efi (for efi systems) or undionly.kpxe (for bios systems) as you would use if using pfsense as dhcp server.

Googlein around gave different options for 067 Bootfile Name but as im usin EFI in Hyper-V ipxe.efi seems to work. Also you need to disable secure boot in Hyper-V settings in client virtual machines.

@george1421

I reinstalled Fog server according to this video: https://www.youtube.com/watch?v=uleFAPmCo7Y

Adjusted Pfsense settings for fog (Thanks for these george) :

Next Server: FOG palvelimen IP
Default BIOS file name: undionly.kpxe
UEFI 32 bit file name: i386-efi/snponly.efi
UEFI 64 bit file name: snponly.efi
ARM 64 bit file name: arm64-efi/snponly.efi

Note: In Hyper-V 1 generation (BIOS) virtual machines work just fine… BUT you have to disable secure boot if you use 2nd gen virtual machines.

@george1421
Thanks
Im pretty sure i have those settings in place but i will check them when im back at office next monday.
Pfsense, Fogserver and workstarion are in same lan segment so problem cannot be in firewall rules either.

I am experiencing this problem also. Same setup in hyper-v environment.